Experimental Study on the Piping Erosion Mechanism of Gap-Graded Soils Under a Supercritical Hydraulic Gradient

2021 ◽  
Author(s):  
Liang Chen ◽  
Yu Wan ◽  
Jian-Jian He ◽  
Chun-Mu Luo ◽  
Shu-fa Yan ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Unsteady Flow ◽  
Relative Density ◽  
Flow Velocity ◽  
Steady Flow ◽  
Fine Particle ◽  
Failure Process ◽  
Hydraulic Gradient ◽  
Particle Content ◽  
Piping Erosion

Abstract Seepage-induced piping erosion is observed in many geotechnical structures. This paper studies the piping mechanism of gap-graded soils during the whole piping erosion failure process under a supercritical hydraulic gradient. We define the supercritical ratio Ri and study the change in the parameters such as the flow velocity, hydraulic conductivity, and fine particle loss with Ri. Under steady flow, a formula for determining the flow velocity state of the sample with Ri according to the fine particle content and relative density of the sample was proposed; during the piping failure process, the influence of Rimax on the rate at which the flow velocity and hydraulic conductivity of the sample increase as Ri decreases was greater than that of the initial relative density and the initial fine particle content of the sample. Under unsteady flow, a larger initial relative density corresponds to a smaller amplitude of increase in the average value of the peak flow velocity with increasing Ri. Compared with the test under steady flow, the flow velocity under unsteady flow would experience abrupt changes. The relative position of the trend line L of the flow velocity varying with Ri under unsteady flow and the fixed peak water head height point A under steady flow were related to the relative density of the sample.

scholarly journals Investigation on the Drag Coefficient of the Steady and Unsteady Flow Conditions in Coarse Porous Media

2021 ◽  
Author(s):  
Hadi Norouzi ◽  
Jalal Bazargan ◽  
Faezah Azhang ◽  
Rana Nasiri
Keyword(s):  
Reynolds Number ◽  
Porous Media ◽  
Friction Coefficient ◽  
Unsteady Flow ◽  
Drag Coefficient ◽  
Flow Velocity ◽  
Hydraulic Gradient ◽  
Flow Conditions ◽  
Porous Media Equations ◽  
Unsteady Flow Condition

Abstract The study of the steady and unsteady flow through porous media and the interactions between fluids and particles is of utmost importance. In the present study, binomial and trinomial equations to calculate the changes in hydraulic gradient (i) in terms of flow velocity (V) were studied in the steady and unsteady flow conditions, respectively. According to previous studies, the calculation of drag coefficient (Cd) and consequently, drag force (Fd) is a function of coefficient of friction (f). Using Darcy-Weisbach equations in pipes, the hydraulic gradient equations in terms of flow velocity in the steady and unsteady flow conditions, and the analytical equations proposed by Ahmed and Sunada in calculation of the coefficients a and b of the binomial equation and the friction coefficient (f) equation in terms of the Reynolds number (Re) in the porous media, equations were presented for calculation of the friction coefficient in terms of the Reynolds number in the steady and unsteady flow conditions in 1D (one-dimensional) confined porous media. Comparison of experimental results with the results of the proposed equation in estimation of the drag coefficient in the present study confirmed the high accuracy and efficiency of the equations. The mean relative error (MRE) between the computational (using the proposed equations in the present study) and observational (direct use of experimental data) friction coefficient for small, medium and large grading in the steady flow conditions was equal to 1.913, 3.614 and 3.322%, respectively. In the unsteady flow condition, the corresponding values of 7.806, 14.106 and 10.506 % were obtained, respectively.

scholarly journals Effect of Clay on Internal Erosion of Clay-Sand-Gravel Mixture

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Chen Liang ◽  
Cai Guo-dong ◽  
Gu Jia-hui ◽  
Tan Ye-fei ◽  
Chen Cheng ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Fine Particle ◽  
Fine Particles ◽  
Fine Sand ◽  
Hydraulic Gradient ◽  
Internal Erosion ◽  
Engineering Project ◽  
Critical Flow Velocity ◽  
Critical Hydraulic Gradient ◽  
Mixture Samples

In this study, a one-dimensional seepage test apparatus was used to investigate the effect of clay on the critical hydraulic gradient, hydraulic conductivity, migration of fine particles in soil, and percentage of fine particle loss during the internal erosion of clay-sand-gravel mixture, compared with clean gravel. The critical hydraulic gradient and fine sand loss percentage of the clay-sand-gravel mixture decreased, and critical flow velocity and the hydraulic conductivity increased. Six clay-sand-gravel mixture samples with different clay contents were used to evaluate the effect of different clay contents on internal erosion. As the percentage of clay mass to fine particle mass increases from 0% to 25%, the critical hydraulic gradient of soil samples decreases by nearly half and the fine sand loss percentage decreases from 13.73% to 3.48%. Overall, clay has a significant effect on the development of internal erosion of clay-sand-gravel mixture. And attention should be paid in engineering project; clay-sand-gravel mixture with a small amount of clay is more likely to be damaged than clean gravel.

scholarly journals Erosion Rate of Lateral Slope Deposit Under the Effects of Different Influencing Factors

2021 ◽  
Vol 9 ◽  
Author(s):  
Yonggang Ge ◽  
Xiaojun Guo ◽  
Meiqiang Zhan ◽  
Hua Yan ◽  
Yansen Liao ◽  
...  
Keyword(s):  
Bulk Density ◽  
Influencing Factors ◽  
Fine Particle ◽  
Erosion Rate ◽  
Failure Process ◽  
Erosion Process ◽  
Particle Content ◽  
Channel Slope ◽  
Time Required ◽  
Inflow Discharge

Lateral slope deposits along a channel represent an important source of material for initiation and development of debris flows/floods that are typically observed in many headwater tributaries. This study found that the failure process of such a deposit reflects combined interaction between external hydrodynamic factors (inflow discharge and channel slope) and internal factors (compactness and fine particle content). The erosion process comprises two stages: runoff erosion toward the toe of the deposit body and soil failure owing to gravity. Spatially, the erosion rate is distributed unevenly across the deposit; the highest value occurs at the section close to the middle of the deposit, on the upstream face. Temporally, the erosion rate decreases exponentially. Overall, the average erosion rate decreases (increases) with bulk density (inflow discharge and channel slope). However, a slope of 7 is a threshold at which the tendency of the erosion rate in relation to the fine particle content differs. In comparison with the other three influencing factors, the effect of the fine particle content is much smaller. Although the bulk density of the deposit imposes the most significant effect, it is of the same order as that of both inflow discharge and channel slope. As the failure process can be summarized as repeated runoff scouring of the toe of the deposit, deposit failure, and entrainment of the failure body by runoff, we proposed a calculation method for the total time required for a complete lateral erosion process, and validation of the calculation suggested its reasonability. The findings of this study enhance the understanding of the mechanism of lateral soil deposit failure, which could help improve runoff-induced debris flood forecasting in headwater regions of mountainous catchments.

scholarly journals Investigation on the Drag Coefficient of the Steady and Unsteady Flow Conditions in Coarse Porous Media

2021 ◽  
Author(s):  
Hadi Norouzi ◽  
Jalal Bazargan ◽  
Faezah Azhang ◽  
Rana Nasiri
Keyword(s):  
Reynolds Number ◽  
Porous Media ◽  
Friction Coefficient ◽  
Unsteady Flow ◽  
Drag Coefficient ◽  
Flow Velocity ◽  
Hydraulic Gradient ◽  
Flow Conditions ◽  
Porous Media Equations ◽  
Unsteady Flow Condition

Abstract The study of the steady and unsteady flow through porous media and the interactions between fluids and particles is of utmost importance. In the present study, binomial and trinomial equations to calculate the changes in hydraulic gradient (i) in terms of flow velocity (V) were studied in the steady and unsteady flow conditions, respectively. According to previous studies, the calculation of drag coefficient (Cd) and consequently, drag force (Fd) is a function of coefficient of friction (f). Using Darcy-Weisbach equations in pipes, the hydraulic gradient equations in terms of flow velocity in the steady and unsteady flow conditions, and the analytical equations proposed by Ahmed and Sunada in calculation of the coefficients a and b of the binomial equation and the friction coefficient (f) equation in terms of the Reynolds number (Re) in the porous media, equations were presented for calculation of the friction coefficient in terms of the Reynolds number in the steady and unsteady flow conditions in 1D (one-dimensional) confined porous media. Comparison of experimental results with the results of the proposed equation in estimation of the drag coefficient in the present study confirmed the high accuracy and efficiency of the equations. The mean relative error (MRE) between the computational (using the proposed equations in the present study) and observational (direct use of experimental data) friction coefficient for small, medium and large grading in the steady flow conditions was equal to 1.913, 3.614 and 3.322%, respectively. In the unsteady flow condition, the corresponding values of 7.806, 14.106 and 10.506 % were obtained, respectively.

Main Characteristics of an Aquifer The main function of the aquifer is to provide underground storage for the retention and release of gravitational water. Aquifers can be characterized by indices that reflect their ability to recover moisture held in pores in the earth (only the large pores give up their water easily). These indices are related to the volume of exploitable water. Other aquifer characteristics include: • Effective porosity corresponds to the ratio of the volume of “gravitational” water at saturation, which is released under the effect of gravity, to the total volume of the medium containing this water. It generally varies between 0.1% and 30%. Effective porosity is a parameter determined in the laboratory or in the field. • Storage coefficient is the ratio of the water volume released or stored, per unit of area of the aquifer, to the corresponding variations in hydraulic head 'h. The storage coefficient is used to characterize the volume of useable water more precisely, and governs the storage of gravitational water in the reservoir voids. This coefficient is extremely low for confined groundwater; in fact, it represents the degree of the water compression. • Hydraulic conductivity at saturation relates to Darcy’s law and characterizes the effect of resistance to flow due to friction forces. These forces are a function of the characteristics of the soil matrix, and of the fluid viscosity. It is determined in the laboratory or directly in the field by a pumping test. • Transmissivity is the discharge of water that flows from an aquifer per unit width under the effect of a unit of hydraulic gradient. It is equal to the product of the saturation hydraulic conductivity and of the thickness (height) of the groundwater. • Diffusivity characterizes the speed of the aquifer response to a disturbance: (variations in the water level of a river or the groundwater, pumping). It is expressed by the ratio between the transmissivity and the storage coefficient. Effective and Fictitious Flow Velocity: Groundwater Discharge As we saw earlier in this chapter, water flow through permeable layers in saturated zones is governed by Darcy’s Law. The flow velocity is in reality the fictitious velocity of the water flowing through the total flow section. Bearing in mind that a section is not necessarily representative of the entire soil mass, Figure 7.7 illustrates how flow does not follow a straight path through a section; in fact, the water flows much more rapidly through the available pathways (the tortuosity effect). The groundwater discharge Q is the volume of water per unit of time that flows through a cross-section of aquifer under the effect of a given hydraulic gradient. The discharge of a groundwater aquifer through a specified soil section can be expressed by the equation:

Hydrology ◽  
2010 ◽  
pp. 229-230
Keyword(s):  
Hydraulic Conductivity ◽  
Flow Velocity ◽  
Darcy’S Law ◽  
Groundwater Discharge ◽  
Effective Porosity ◽  
Darcy's Law ◽  
Hydraulic Gradient ◽  
Water Volume ◽  
Storage Coefficient ◽  
Groundwater Aquifer

Unidirectional to bidirectional subtidal sandwaves influenced by gradually decreasing steady flow velocity

1997 ◽  
Vol 134 (4) ◽  
pp. 557-561
Author(s):  
KATSUHIRO NAKAYAMA
Keyword(s):  
Grain Size ◽  
Flow Velocity ◽  
Steady Flow ◽  
Periodic Flow ◽  
Southwest Japan ◽  
Unit Thickness ◽  
Flow Components ◽  
Flow Velocities

Miocene subtidal sandwave deposits in southwest Japan were influenced by periodic flow and steady flow. The sandwave deposits can be divided into five units, based on lithofacies and thickness. In order of accretion, unit 1 consists of unidirectional sand bedforms without mud drapes, unit 2 of unidirectional sand bedforms with thin, discontinuous mud drapes, unit 3 of bidirectional sand bedforms with thin continuous mud drapes, and units 4 and 5 of relatively thinner and smaller bidirectional sand bedforms with continuous mud drapes. The thickness of units 1 to 3 increase progressively to 2.6 m, and units 4 to 5 subsequently decrease from 2.0 to 1.0 m. Variations between the units are due to differing combinations of periodic and steady flow velocities. Palaeoflow velocity is estimated from grain size and unit thickness. Depth-mean velocities of steady flow components gradually decrease from 0.72 ms−1 to 0.16 ms−1 with unit accumulation.

scholarly journals Propulsion Performance of the Full-Active Flapping Foil in Time-Varying Freestream

2020 ◽  
Vol 10 (18) ◽  
pp. 6226
Author(s):  
Zhanfeng Qi ◽  
Lishuang Jia ◽  
Yufeng Qin ◽  
Jian Shi ◽  
Jingsheng Zhai
Keyword(s):  
Flow Velocity ◽  
Steady Flow ◽  
Navier Stokes ◽  
Time Varying ◽  
Flapping Foil ◽  
Propulsion Performance ◽  
Reduced Frequency ◽  
Motion Parameters ◽  
Volume Method ◽  
The Impact

A numerical investigation of the propulsion performance and hydrodynamic characters of the full-active flapping foil under time-varying freestream is conducted. The finite volume method is used to calculate the unsteady Reynolds averaged Navier–Stokes by commercial Computational Fluid Dynamics (CFD) software Fluent. A mesh of two-dimensional (2D) NACA0012 foil with the Reynolds number Re = 42,000 is used in all simulations. We first investigate the propulsion performance of the flapping foil in the parameter space of reduced frequency and pitching amplitude at a uniform flow velocity. We define the time-varying freestream as a superposition of steady flow and sinusoidal pulsating flow. Then, we study the influence of time-varying flow velocity on the propulsion performance of flapping foil and note that the influence of the time-varying flow is time dependent. For one period, we find that the oscillating amplitude and the oscillating frequency coefficient of the time-varying flow have a significant influence on the propulsion performance of the flapping foil. The influence of the time-varying flow is related to the motion parameters (reduced frequency and pitching amplitude) of the flapping foil. The larger the motion parameters, the more significant the impact of propulsion performance of the flapping foil. For multiple periods, we note that the time-varying freestream has little effect on the propulsion performance of the full-active flapping foil at different pitching amplitudes and reduced frequency. In summary, we conclude that the time-varying incoming flow has little effect on the flapping propulsion performance for multiple periods. We can simplify the time-varying flow to a steady flow field to a certain extent for numerical simulation.

scholarly journals Effects of Hydraulic Gradient and Clay Type on Permeability of Clay Mineral Materials

Minerals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1064
Author(s):  
Masanori Kohno
Keyword(s):  
Hydraulic Conductivity ◽  
Specific Surface ◽  
Surface Area ◽  
Clay Mineral ◽  
Specific Surface Area ◽  
Hydraulic Gradient ◽  
Consistency Index ◽  
Hydrogen Energy ◽  
The Difference ◽  
Mineral Type

Considering the relevance of clay mineral-bearing geomaterials in landslide/mass movement hazard assessment, various engineering projects for resource development, and stability evaluation of underground space utilization, it is important to understand the permeability of these clay mineral-based geomaterials. However, only a few quantitative data have been reported to date regarding the effects of the clay mineral type and hydraulic gradient on the permeability of clay mineral materials. This study was conducted to investigate the permeability of clay mineral materials based on the clay mineral type, under different hydraulic gradient conditions, through a constant-pressure permeability test. Comparative tests have revealed that the difference in the types of clay mineral influences the swelling pressure and hydraulic conductivity. In addition, it has been found that the difference in water pressure (hydraulic gradient) affects the hydraulic conductivity of clay mineral materials. The hydraulic conductivity has been found to be closely associated with the specific surface area of the clay mineral material. Furthermore, the hydraulic conductivity value measured is almost consistent with the value calculated theoretically using the Kozeny–Carman equation. Moreover, the hydraulic conductivity is also found to be closely associated with the hydrogen energy, calculated from the consistency index of clay. This result suggests that the hydraulic conductivity of clay mineral materials can be estimated based on the specific surface area and void ratio, or consistency index of clay.

scholarly journals Relating in situ hydraulic conductivity, particle size and relative density of superficial deposits in a heterogeneous catchment

2012 ◽  
Vol 434-435 ◽  
pp. 130-141 ◽  
Author(s):  
A.M. MacDonald ◽  
L. Maurice ◽  
M.R. Dobbs ◽  
H.J. Reeves ◽  
C.A. Auton
Keyword(s):  
Particle Size ◽  
Hydraulic Conductivity ◽  
Relative Density

scholarly journals Experimental study on water level and absorption capacity in a radial well flow in a loess area

2018 ◽  
Vol 19 (5) ◽  
pp. 1313-1321
Author(s):  
Xuezhen Zhang ◽  
Aidi Huo ◽  
Jucui Wang
Keyword(s):  
Unsteady Flow ◽  
Water Absorption ◽  
Water Level ◽  
Steady Flow ◽  
Flow Injection ◽  
Absorption Capacity ◽  
Water Absorption Capacity ◽  
Analysis Method ◽  
Semi Empirical ◽  
Radial Well

Abstract In this paper, the theoretical basis for flow calculation in an injection well was discussed. It proposed that the flow rate of an injection well could be calculated referring to pumping theory and method. A mathematical model of the rising curve of water level around a radial well was established and the equation for calculating the rising curve was given. The calculation equations selected for the water absorption capacity of injection wells were explained and examples were verified and compared. The results indicated that, under the same injection conditions, the water level value calculated by the analysis method was slightly larger, but the error between the analysis method and the semi-theoretical and semi-empirical methods was small. In the processes of steady flow injection and unsteady flow injection, there was a small difference of water absorption capacity, and the former was slightly larger. The measured values of water absorption capacity were only about one-third of the calculated values based on pumping theory. Overall, the analytical solution method for predicting the rising curve of water level has priority in well injection. The semi-theoretical and semi-empirical equation for calculating water absorption capacity sifted first has priority in steady flow injection, the equation sifted second has priority in unsteady flow injection.

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